The basic mode of operation of an active implantable medical device known as a cardiac prosthesis device is an AAI mode—or more precisely ‘pseudo-AAI mode’—with single chamber atrial pacing (AAI mode in the strict sense) and monitoring of ventricular activity. This mode is normally maintained as long as an atrioventricular conduction is normal, i.e., as long as each atrial event (e.g., atrial detection corresponding to spontaneous activity, atrial pacing corresponding to a stimulation) is followed by an associated ventricular detection.
However, when the device operates in a “dual chamber” mode, after an atrial event—whether it is a spontaneous atrial depolarization (detection of a P wave) or stimulated atrial depolarization (delivery of an A pulse)—the device simultaneously monitors ventricular activity and starts measuring a delay called “atrioventricular delay”, commonly referred to as AVD. If at the end of the AVD, no spontaneous ventricular activity (R wave) is detected, then the device triggers a stimulation of the ventricle (application of a V pulse).
Recent clinical studies have demonstrated that for preventing an occurrence of heart failure or atrial fibrillation among patients with dual chamber pacemakers, it is recommended to avoid as much as possible right ventricular pacing. This is done to preserve an intrinsic AV conduction in patients who have otherwise no permanent conduction disorder requiring the use of a permanent ventricular pacing.
In this respect, recent cardiac prosthesis devices implemented a new stimulation mode that emphasizes a spontaneous ventricular conduction, and permits an operation with a long AVD that increases the time in which a potential spontaneous ventricular conduction may occur—but in return accepts the risk of maintaining the symptomatically long AVD.
Some pacemakers, for example, of the type described in EP 0 488 904 and its US counterpart U.S. Pat. No. 5,318,594 (ELA Medical, now known as Sorin CRM) are equipped with AVD hysteresis algorithms that are used in a DDD mode to stimulate patients not having conduction disorders. These devices can operate in two modes, DDD or AAI (the AAI mode being a DDD mode modified by lengthening the AV delay), and are provided with a mode called “DDD-CAM” providing automatic mode switching (CAM) of DDD to AAI and vice versa. The value of the AVD is not fixed but varies linearly between a maximum value, used when the heart rate is near the rest frequency, and a minimum value, used when the heart rate is near its maximum value. The details of this adaptation of AVD is described for example in EP 1 059 099 A and its US counterpart U.S. Pat. No. 6,622,039 (ELA Medical, now known as Sorin CRM). The basic idea of the AVD hysteresis algorithm is to extend the value of AVD under certain criteria, to which favors the occurrence of a potential spontaneous rhythm: the AVD can thus be lengthened to avoid unnecessary ventricular pacing or gradually reduced if no spontaneous rhythm is found, to return to a normal value of conventional DDD stimulation.
This technique preserves the natural conduction in some patients, but has been found to be of a limited use in other patients especially those with sinus dysfunction because the limits of the hysteresis make it difficult to discover the spontaneous rhythm.
To overcome this limitation, a new pacing mode called “AAIsafeR” has been developed in more recent devices, whose basic principle is explained in EP 1 346 750 and its US counterpart U.S. Pat. No. 7,164,946 (ELA Medical, now known as Sorin CRM). In an AAIsafeR mode, the device operates in an AAI mode and the ventricular activity is constantly monitored to detect an occurrence of atrioventricular blocks (AVB) that cause a temporary disorder of depolarization of the ventricle. In this case, because a number of conditions are met, the device automatically switches to a DDD mode, with operating parameters optimized for this temporary AVB condition. In a multisite device, the switching is instead made to a biventricular stimulation mode (also referred to as a “BiV” mode), named “AAISafeRR”. After the AVB condition disappeared, and thus the atrioventricular conduction was restored, the device automatically returns to the AAI mode when a number of other conditions are met. The AAIsafeR (or AAISafeRR) mode also includes a switching criterion linked to the detection of an AV block of the first type or AVB1, that is to say, the presence of a too long AVD: when the device detects, for example, more than six consecutive cycles of a too long AVD (typically longer than 350-450 ms), then the device switches to a DDD mode, or in a similar way, to a biventricular mode on a multisite device.
The AAIsafeR (or AAISafeRR) mode preserves the natural conduction very efficiently, and the clinical results show a percentage of residual ventricular pacing close to zero. Various improvements have been made, for example, to eliminate an incidence of premature ventricular contractions (See EP 1 470 836 and its US counterpart U.S. Pat. No. 7,076,297 (ELA Medical, now known as Sorin CRM)) and/or paroxysmal AV block (See EP 1 550 480 A and its US counterpart U.S. Pat. No. 7,366,566 (ELA Medical, now known as Sorin CRM), or in the presence of ventricular events of uncertain nature occurring during the safety window (See EP 1 731 195 A and its US counterpart U.S. Published Application No. 2007/0135849. ELA Medical, now known as Sorin CRM), or in the presence of ventricular tachycardias (See EP 1 731 194 A and its US counterpart U.S. Publication No. 2007/0135850, ELA Medical, now known as Sorin CRM).
One of the peculiarities of the AAIsafeR (or AAISafeRR) pacing mode is to allow a very long AVD, which is programmable. But such delays can be more or less well tolerated by the patient, or can be tolerated under certain conditions (e.g., at rest) and less tolerated in others (e.g., during exercise). In patients suffering from brady-tachycardia and taking anti-arrhythmic drugs, an appearance of symptoms related to a too long AVD in AAI mode were notably reported.
In some patients, the risk of stimulating the right ventricle too often must be balanced with the risk of developing symptoms by the use of a too long AVD. In the absence of specific criteria, this risk is assessed as a function, for example, of the patient's ejection fraction, and possibly based on symptoms reported at follow-up visits, but, in any event, is never based on the instantaneous situation of the patient.
Moreover, these difficulties linked to a too long AVD time may be only transient and only occur, for example, during certain patient activity, or only for some patients during atrial pacing and not after a spontaneous P wave. In such cases, it would be detrimental to permanently program a short AVD to overcome these transients.
It is therefore, an object of the present invention to provide a cardiac prosthesis device equipped with a pacing mode favoring a spontaneous conduction of a patient (including a device of the AVD hysteresis type or a device of the AAIsafeR (or AAISafeRR type), which overcomes the difficulties and limitations outlined above, related to considered a long AVD in case of AVB1.